1. Field of the Invention
The present invention relates to a soft magnetic member having superior magnetic characteristics, a reactor using the soft magnetic member, a powder for a dust core, and a method of producing a dust core.
2. Description of Related Art
In a hybrid vehicle, an electric vehicle, a solar power generation device, or the like, a reactor is used, and this reactor adopts a structure in which a coil is wound around a ring-shaped core which is a soft magnetic member. During use of the reactor, a wide range of currents flow through the coil. Therefore, at least 40 kA/m of magnetic field is applied to the core. In such an environment, it is necessary to stably secure the inductance of the reactor.
In consideration of the above-described points, for example, a reactor 9 is disclosed in which, as shown in FIG. 9A, a ring-shaped core 91 is divided into core portions 92A, 92B, a gap 93 is provided between the divided core portions 92A, 92B, and coils 95A, 95B are wound around the core 91 including this gap 93 (for example, refer to Japanese Patent Application Publication No. 2009-296015 (JP 2009-296015 A)).
According to the reactor 9, the gap 93 is provided between the divided core portions 92A, 92B; as a result, even when a wide range of currents flow through the coil 95 of the reactor 9, the inductance can be stably secured in this wide range of currents.
However, a soft magnetic member is used in a choke coil, an inductor, or the like. As such a soft magnetic member, a dust core is disclosed in which, when an initial magnetic permeability is represented by μ0 and a magnetic permeability in an applied magnetic field of 24 kA/m is represented by a relationship of μ/μ0≥0.5 is satisfied between μ0 and μ (for example, refer to Japanese Patent Application Publication No. 2002-141213 (JP 2002-141213 A)). According to this dust core, even if a high magnetic field is applied to the dust core, a decrease in the magnetic permeability of the dust core can be suppressed.
However, for example, in the technique disclosed in JP 2009-296015 A, the gap is formed between the divided core portions. Therefore, as shown in FIG. 9B, a magnetic flux T is leaked in the gap 93 formed between the divided core portions 92A, 92B. In particular, in a reactor of a hybrid vehicle or the like through which a high current flows, a high magnetic field of about 40 kA/m is applied to a core. Therefore, in order to maintain the inductance of the reactor (that is, the core) at the applied magnetic field, it is necessary to further increase the above-described gap. As a result, the leakage of the magnetic flux T from the gap is increased, and this leaked magnetic flux intersects with the coil, which causes eddy-current loss in the core.
The problem which is described above using the reactor is an example. In equipment or an apparatus in which a magnetic field in a range from a low magnetic field to a high magnetic field (40 kA/m) is applied to a soft magnetic member, it is difficult to maintain the inductance, and typically a structural measure is taken.
Even if a soft magnetic member having the characteristics disclosed in JP 2002-141213 A is used, as clearly seen from an experiment of the present inventors described below, the application of a high magnetic field of about 40 kA/m is not considered. Therefore, even if such a material is used, a significant decrease in inductance is assumed in a high magnetic field (about 40 kA/m).